We don't have support for the GPR RAW format from GoPro. It appears to be yet another TIFF-based RAW file. I parsed through the file but found no embedded thumbnail nor JPEG preview, so even if we added support for this format we wouldn't be able to show you anything since we do not render RAW.
My suggestion is to convert to DNG then PM should let you browse those files. Just make sure you configure DNG Converter Preferences to embed a full resolution preview. Note: when I did this for your sample file, I noticed that the DNG was mirrored horizontally. Is this a setting in the camera? If so, then even if you convert to DNG then PM will not "un-mirror" the image so it will be backwards left-to-right. I'll see if we can resolve this issue.
Is there an option in the GoPro to generate a JPEG preview with their GPR format? That would be the way to go. Then we may be able to support this camera natively without having to do a DNG conversion.